1. Field of the Invention
The present invention relates to a buildup welding apparatus and a welding method for a thick plate by a laser beam.
2. Description of the Related Art
With respect to welding of a thick plate of steel, nickel base alloy and the like, a method of forming a groove in a welding section and filling the groove by buildup welding of a plurality of passes while feeding a filler metal such as a welding wire and welding rod is commonly adopted, however, because the cross-sectional area of the groove increases as the plate thickness increases, the method involves problems such as drop of the manufacturing efficiency due to increase in the number of weldpass and degradation of the welding quality due to increase of deformation and welding distortion.
Therefore, narrow groove welding methods narrowing the groove and reducing the required deposited metal amount have been developed, and with respect to a heat source also, such efforts of improving the directivity of an arc, adopting a laser beam with high focusing performance, and the like to cope with narrowing of the groove have been made. With respect to the laser particularly, output power and focusing performance have been remarkably improved due to the progress of oscillators in recent years, and as described in the Japanese Unexamined Patent Application Publication No. H09-201687 for example, narrowing of the groove that has never been achieved by a conventional heat source for an arc is possible.
According to narrow groove welding by a laser described above, the convergence of energy is high, and therefore the width of the formed weld bead generally becomes narrower than that in arc welding. On the other hand, the shape of the groove is determined so as to avoid interference with the laser beam, whereas the laser beam is irradiated to the bottom of the groove from a focusing lens with a constant converging angle according to the focal length of the lens, and therefore, as the plate thickness of the welding section increases and the depth of the groove becomes deeper, the required width at the upper part of the groove becomes larger. Accordingly, there was a problem that, even if sound welding of one pass per one layer was possible in the lower part of the groove, lack of fusion was liable to occur between the wall of the groove and the weld bead as building up progressed to the upper part of the groove.
Also, in the laser narrow groove welding, there was a problem that the solid filler metal such as a welding wire and welding rod was liable to be fed in a state shifted to the direction of the side wall of the groove because the width of the groove was small, and the deposited metal formed shiftingly to the side wall direction became an obstacle in feeding the filler metal in welding the following layer, which impeded sound welding.
Further, in the laser narrow groove welding, there was a problem that metal gas that was generated by irradiation of the laser beam filled inside the narrow groove, scattered the laser beam, and lowered the heat input efficiency to the welding section. The object of the present invention is to solve the problems of the conventional technology described above.
(Means to Solve the Problems)